Some known electric circuits include contactors that control the flow of current through the circuit. The contactors control current flow through the circuit by opening or closing a conductive pathway that extends through the contactor to correspondingly open or close the circuit.
In circuits that convey relatively high levels of direct current, electric arcs will be generated inside the contactors when the contactor switches from a closed state to an open state to open the circuit. When the contactors change from the closed state to the open state, an electric arc will radiate from the contacts in the contactor while the current is being driven to zero by the resistance of the arc. The electric arc can be of relatively high energy. If the arc is of sufficiently high energy and time duration, the arc can damage and/or contaminate the contacts in the contactor. The arcs also can weld the contacts with one another if arcs are present during contact bouncing during the closing operation. For example, the arcs may weld the contacts together such that the contactor cannot separate the contacts to open the circuit to which the contactor is connected.
Some known contactors that are able to withstand relatively large surges of current are large, heavy and expensive to manufacture. The contactors may include relatively large contacts, actuator mechanisms and/or arc dissipation members that are heavy and/or expensive to produce. Other smaller and/or lighter contactors are unable to withstand relatively large currents due to the small contact forces combined with the placement of the arc magnets. Also, the contacts and/or arc dissipation members in these contactors are more easily damaged by the electrical arcs radiating from the contacts. Additionally, some of the contacts may be separated from one another and open the circuit when the contacts are subjected to large surge currents. The arc that emanates due to those events may result in a catastrophic arc event, or welding of contacts upon re-closure.
In some power switching contactors, arc control is facilitated by the use of permanent magnets. However, in many such devices, the magnets are placed such that the device is polarity sensitive to the interrupting current. In addition, the positioning of the permanent magnet interacts with the magnetic field of the contact such that when the contacts are closed and conducting current, the contact force is reduced beyond that due to the normal contribution of the contact spot repulsive force. U.S. Pat. No. 8,232,499 discloses contactor assembly having permanent magnets. A contactor assembly is adapted for switching power to a circuit having a power source. The contactor assembly includes a housing, carry contacts and arc contacts. The housing defines an interior compartment and includes internal chamber walls that laterally extend within the compartment to define a protection chamber. The carry contacts are disposed in the protection chamber of the housing. The arc contacts are disposed in the housing outside of the protection chamber. The internal chamber walls of the housing prevent material that is expelled from one or more of the arc contacts when an electric arc emanates from one or more of the arc contacts from contaminating one or more of the carry contacts. Magnets may be provided on opposite sides of the interior compartment alongside or adjacent to the lateral perimeter walls. The magnets create magnetic flux or a magnetic field that extends across or encompasses the arc contacts. With the magnetic flux, the flux alters the path of the arc, thereby effectively increasing the distance that the arc must travel.
While the contactor assembly of U.S. Pat. No. 8,232,499 provides adequate arc control, a need exists for a smaller, lighter and/or less expensive contactor that is able to safely turn on and off relatively large electric currents while avoiding welding and excessive arcing damage to the contacts in the contactor. In addition, there exists a need for an arc control which is insensitive to polarity and which does not result in a reduction of contact forces when the contacts are moved to the closed position.